Multiple tube finning apparatus

ABSTRACT

A tool for producing either a two or three lead integral fin structure on thin wall tubing is provided with two or more arbors, each having three groups of finning discs which are spaced from each other by a first and a second spacer. The second group of discs is located between the two spacers and includes a first disc adjacent the first spacer having a diameter of less than the diameter of the last disc on the first group. The second group of discs also includes a last disc adjacent the second spacer having a diameter greater than the diameter of the first disc on the third group adjacent the second spacer. In addition, the second group of discs includes another disc which is disposed intermediate the first and last discs and has a diameter which is substantially equal to that of the last disc on the first group and the first disc on the third group. At least two, and preferably three, arbors are employed and spaced during finning so that they begin separate fin leads.

United States Patent [1 1 Kallfelz et al.

[451 July 17,1973

[ MULTIPLE TUBE FINNING APPARATUS [75] Inventors: Albert J. Kallfelz, Camillus; Carl J.

Schmeling, Liverpool, both of N.Y.

[73] Assignee: Carrier Corporation, Syracuse, N.Y.

[22] Filed: Mar. 2, 1972 21 Appl. No.: 231,295

Primary Examiner-Lowell A. Larson Attorney-Harry G. Martin, Jr. and J. Raymond Curtin [57] ABSTRACT A tool for producing either a two or three lead integral fin structure on thin wall tubing is provided with two or more arbors, each having three groups of finning discs which are spaced from each other by a first and a second spacer. The second group of discs is located between the two spacers and includes a first disc adjacent the first spacer having a diameter of less than the diameter of the last disc on the first group. The second group of discs also includes a last disc adjacent the sec ond spacer having a diameter greater than the diameter of the first disc on the third group adjacent the second spacer. In addition, the second group of discs includes another disc which is disposed intermediate the first and last discs and has a diameter which is substantially equal to that of the last disc on the first group and the first disc on the third group. At least two, and preferably three, arbors are employed and spaced during finning so that they begin separate fin leads.

9 Claims, 3 Drawing Figures MUL'llLE TUBE FlNNllNG APPARATUS BACKGROUND OF THE INVENTION This invention relates to tube finning apparatus and more particularly to an apparatus employing a finning tool having a unique combination of finning discs and spacers which make it especially satisfactory for producing multi-lead fins.

In U. S. Pat. No. 3,600,922, there is described a tool having three groups of finning discs which is highly satisfactory for providing single-lead fins on thin wall tub ing. However, it is becoming increasingly desirable to provide double or triple-lead fins on tubing, both because of superior heat transfer characteristics and because the multi-lead fins can be made at a faster rate than single-lead fins. It would seem logical to simply pair up the finning discs on the tool shown in the aforementioned patent in order to form a double-lead fin. However, it has been found in practice that this approach is not feasible because long tool strings appear to flex out of shape and distort the fin. Also, the many pairs of discs required result in an excessively expensive tool which wears quickly and is subject to frequent failure due to breakage. Furthermore, increasing the number of tools seems to result in excessive work hardening of the tube which produces unsatisfactory fins. While the precise dynamics involved in such a tube finning operation are not entirely understood, it is known that contacting a thin wall tube being finned with a tool having a large number of discs results in such great torsional stress on the tube that it often splits open. Consequently, it has been necessary to use thicker, more expensive tubing to provide a satisfactory multiple lead fin. To some extent, this stress can be relieved by providing spacers in the tool string which seems to enable a period of time to expire during which the tube relaxes before the finning operation is again continued. However, it has been discovered that other changes also seem to take place in the tube during the relaxation period and that the diameter of the root being formed actually grows sufiiciently to result in an excessively stressed tube or fin when it is thereafter contacted by a disc of substantially the same diameter as the preceding disc. It has also been found to be desirable to avoid excessive pairing up of discs and to employ as few a number of discs in the tool as possible, both to reduce the overall length and cost of the tool and prevent excessive tool flexing and to prevent excessive work hardening of the tube. It would also be desirable to provide a tool which can form either double or triple-lead fins.

Accordingly, it is a principal object of the invention to provide an improved apparatus for forming multiple lead fins on thin wall tubing having relative disc diameters which overcome prior difficulties in tube finning apparatus.

SUMMARY OF THE lNVlENTlON In accordance with this invention, it has been found that an improved tool for manufacturing multi-lead integral fins on thin wall tubing which overcomes the above disadvantages, is provided by separating the tube finning discs into three spaced relatively short groups of discs having a pair of spacers to divide the groups, wherein the second group of discs includes a first disc adjacent the first spacer having a diameter smaller than the diameter of the largest disc in the first group, a larger disc having a diameter larger than the smallest disc of the third group of discs, and preferably having an intermediately placed disc having a diameter which is substantially equal to the diameter of the last disc in the first group and the first disc in the last group.

The arrangement of disc. diameters described results in a highly satisfactory multiple lead finned tubing without encountering the difficulties of excessive work hardening and tube twisting which have been associated with other tool configurations for multi-lead finning. The exact reasons for this superiority are not entirely known, but it has been reasoned that the combination of a time lapse between the tool groups and the engagement by a disc of smaller diameter as the last disc of the preceding group may provide the tube an opportunity to become unstressed during the finning operation and allow the root diameter of the fin an opportunity to grow in diameter during the period of relaxation so that contacting the groove with a smaller diameter disc after the relaxation period decreases the work done by that disc and reduces work hardening and stress failures caused by excessive fin deformation. Further, this particular middle group of discs disposed between two spacers, seems to create a smoother transition from the root forming first group to the fin shaping third group so that fewer total discs are required.

BlRlElF DESClRlPTlON OF THE DRAWINGS FlG. 1 illustrates in cross section a tube being finned passing between three tool carrying arbors;

IFllG. 2 illustrates the relationship of one of the fin carrying arbors with the tube being finned; and

Fit}. 3 illustrates in exaggerated scale the relative diameters of the discs comprising one of the fmning tools.

DESCRIPTKON OF THE PREFERRED EMBODIMENT Referring to the drawing, there is shown three rotatable arbors ltl, ll, l2 which are circumferentially spaced apart and carry a plurality of finning discs D keyed thereon by splines in, 117, lb respectively and held thereon by fastening nut 22. The arbors are skewed at a slight angle in each direction to the axis of a tube 19 which is advanced through the apparatus. Rotation of the arbors in the same direction causes the discs on each of the arbors to successively engage the periphery of tube l9 to form and shape a helical fin formation 2d thereon and to advance the tube in a manner which is well known in the art.

Each arbor carries an identical set of discs and the discs on each arbor are divided into three groups of discs 25, 26, 27 by a first spacer 2% and a second spacer 2f Spacer 2% has a length greater than the thickness of at least three, and preferably four, finning discs by an amount which compensates for the tube elongation after contact with group 25 and relaxation during the interval provided by the spacer. Spacer 29 has a length which is greater than the thickness of at least three, and preferably five, finning discs by an amount to compensate for the axial elongation of the tube after contact with group 2% and the subsequent relaxation.

For convenience in describing the tool string, discs of the same or substantially the same diameter are designated with the same reference numeral and the reference numerals are applied in the order of increasing diameter. First group 25 of discs includes a relatively small disc ill which is the first disc to engage a prime surface tube being advanced through the apparatus by rotation of the arbors. The following discs 41, 42 and 43 are of successively greater diameter.

The second group of discs 26 includes a first disc 42 adjacent first spacer 28 having a diameter smaller than the diameter of last discs 43 of first group 25 which is also adjacent spacer 28. Second group 26 has a last disc 44, adjacent spacer 29, larger than first disc 42 of second group 26, and which has a diameter greater than that of first disc 43 of third group 27. Second group 26 also has another disc 43 axially spaced between discs 43 and 44 which has a diameter substantially equal to the diameter of the last disc in first group 25 and the first disc in third group 27.

Third group 27 includes a first disc 43 adjacent spacer 29 having a diameter substantially equal to the middle disc of group 26 and a second disc having a diameter substantially equal to the diameter of the last disc in group 26. Third group 27 also includes third and fourth discs 45, 46 of successively larger diameters and the final three discs of the third group are substantially equal in diameter to that of fourth disc 46.

The discs generally have peripheral edges of increased angularity to the arbor axis and broadened transverse peripheral thickness toward the last disc 46 of the tool string to provide the desired shape to the fin as is well known in the art. For example, the final pair of discs 46 are broader than the preceding pair of discs 46. The relative diameters of the various discs are exaggerated in the drawing for clarity and preferred diameters are given in the following table for making a double-lead, 23 fins per inch formation on 0.049 inch wall 0.745 inch diameter tubing.

Disc Diameter Disc Diameter 40 2.029 44 2.077 41 2.041 45 2.088 42 2.053 46 2.095 43 2.065

It will be seen that the tool illustrated in FIG. 3 consists of only 14 discs which makes a relatively short tool string that is generally free from excessive flexing during operation.

When it is desired to form a double-lead fin on the tubing being advanced through the apparatus, arbor 10 is positioned so that the first disc 40 of arbor 12 is axially spaced by an amount equal to about one disc thickness from the first discs of arbors l and 11. Consequently, a first groove is formed in the tube wall by the first disc of arbor l0 and the second groove is thereafter formed by the first disc on arbor ll. Arbor 12 is positioned axially with respect to arbors l0 and 11 so that the first disc on arbor 12 contacts the same groove as that being formed by the first disc on arbor 11 in the case of a two-lead fin. In the illustrated embodiment, the groove being formed by the first disc 40 on arbor will next be contacted by the second disc 41 on arbors 11 and 12 and will then be contacted by fourth disc 43 on arbor 10 and so on down the tool string. The second groove, being formed by the first disc 40 on arbor 11, will next be contacted by the first disc 40 on arbor l2 and then by third disc 42 on arbor 10 and so on down the tool string of each arbor.

If, however, it is desired to form a three-lead fin on tube 19, all three arbors 10, 11 and 12 are axially spaced relative to each other so that corresponding tube engaging portions lie in the same vertical plane with respect to the axis of the tube being finned. Under these circumstances, first disc 40 on each of arbors 10, l

11 and 12 will begin a separate groove which will successively be contacted by the second disc on the next arbor and the third disc on the third arbor and so forth down the tool string on each arbor.

It will be seen that in either type of operation, the fins being formed eventually contact the fourth disc 43 on one of the arbors and are thereafter given a period of time equal to at least the distance of three, and preferably four, discs in which the metal is enabled to relax after the initial groove forming. During this period of time, the torsion on the tube is believed to be relieved and the root of the grooves being formed increase in diameter. It has been found that if the groove is next contacted by a disc on the next group of the same diameter as the preceding discs, there is a tendency for the fin to be folded over, ultimately resulting in excessive work hardening of the fin. For this reason, disc 42, which is the first disc on the second group, is made smaller than the last disc on the first group because it seems to be necessary to reform the fin after the period of relaxation. Likewise, the last disc 44 on the second group is made larger than the first disc 43 on the third group with a spacer provided therebetween so that additional relaxation of the tube and increase in the root diameter will not result in excessive interference with the first disc on the third group.

It is a unique advantage of the tool illustrated herein that either a double-lead or a triple-lead fin can be provided with the same set of tools having a relatively few number of discs.

It has been found that the provision of the second group of discs between the spacers, having the relative diameters illustrated, also results in more balanced tool wear and a lessening of the total number of tools required in a multi-lead fin forming operation. The relatively few discs required by this tool result in a sharp fin having less work hardening failures and enabling a higher speed finning operation with less tool breakage. Furthennore, the arrangement described provides a desirably unifonn amount of tool wear so that an opti mum life for the tool string is achieved in production. Also, torsion failures are greatly reduced by the arrangement of discs and spacers described.

Various other modifications of this invention will be appreciated from the foregoing description. For example, it is possible to pair up disc 41 in group 25 and discs 43 and 44 in second group 26 to provide a satisfactory double-lead fin, which arrangement, it will be seen, retains the relationship between the first, last and intermediate discs in second group 26 with the last disc of group 25 and first disc of group 27. Also, a different number of arbors may be employed with or without idler rolls if desired. Accordingly, this invention may be otherwise embodied within the scope of the following claims.

We claim:

1. Apparatus for forming a multiple lead helical fin formation on tubing which comprises:

A. a plurality of arbors positioned in circumferentially spaced relation around the axis along which a tube advances during a progressive finning operation, said arbors being positioned at an angle to said tube axis;

B. a plurality of finning discs mounted on each of said arbors for rotation therewith, said finning discs being mounted in three spaced groups of discs which sequentially engage a tube advanced through the apparatus;

C. a pair of spacers mounted on each of said arbors, the first of said spacers separating the first group of discs to engage a tube advanced through the apparatus from the second group of discs to engage the tube, and the second of said spacers separating the second group of discs from the third group of discs to engage the tube, said spacers having an axial length sufficient to separate said groups of discs a distance greater than the thickness of at least three of the discs to provide a period of time between contact of a portion of the tube surface by the discs of the successive groups;

D. the second of said three groups of discs including:

1. a first disc adjacent said first spacer of a diameter less than the diameter of the largest disc of the first group of discs to engage the tube;

2. said second group of discs including a last disc having a diameter greater thanthe diameter of the first disc of the second group of discs and larger than the diameter of the first disc adjacent said second spacer of the third group of discs to engage the tube; and

3. said second group having another disc disposed intermediate said first disc and said second disc thereof, said other disc having a diameter intermediate the diameter of said first'disc and said last disc of the second group of discs.

2. An apparatus for forming multiple lead helical fin formations as defined in claim 1, wherein the last disc on said first group of discs has a diameter substantially equal to the diameter of the first disc on the third group of discs, and wherein said other disc of said second group of discs has a diameter substantially equal to the diameter of the last disc of the first group and the first disc of the third group.

3. An apparatus for forming multiple lead helical fin formations as defined in claim 1, wherein each of said arbors consists of identical sets of discs.

4. An apparatus for forming multiple lead helical fin formations as defined in claim 1 wherein each of said three groups of discs on each arbor comprise at least three discs of progressively increasing diameter.

5. An apparatus for forming multiple lead helical fin formations as defined in claim 1 wherein at least two of said arbors are axially located with respect to each other so that the tube engaging portions of corresponding discs lie in a plane perpendicular with the axis of the tube so that at least two leads of said fin formation are simultaneously formed by the first disc on different arbors.

6. An apparatus for forming multiple lead helical fin formations as defined in claim I wherein said apparatus includes three of said arbors having identical sets of discs thereon, such arbors being axially located with respect to each other so that the tube engaging portions of corresponding discs lie in a plane perpendicular to the axis of the tube whereby three leads of said fin formation are simultaneously formed by the first disc on each of said three arbors.

7. Apparatus for forming a multiple lead helical fin formation on tubing which comprises:

A. a plurality of arbors positioned in circumferentially spaced relation around the axis along which a tube advances during a progressive finning opera tion, said arbors being positioned at an angle to said tube axis;

B. a plurality of finning discs mounted on each of said arbors for rotation therewith, said finning discs being mounted in three spaced groups of discs which sequentially engage a tube advanced through the apparatus;

C. a pair of spacers mounted on each of said arbors, the first of said spacers separating the first group of discs to engage a tube advanced through the apparatus from the second group of discs to engage the tube, and the second of said spacers separating the second group of discs from the third group of discs to engage the tube, said spacers having an axial length sufficient to separate said groups of discs a distance greater than the thickness of at least three of the discs to provide a period of time between contact of a portion of the tube surface by the discs of the successive groups;

D. the second of said three groups of discs including: 1. one disc having a diameter less than the diameter of the largest disc of the first group of discs to engage the tube;

2. said second group of discs including another disc having a diameter greater than the diameter of said one disc of the second group and larger than the diameter of the smallest disc of the third group of discs to engage the tube, said other disc being arranged in said second group of discs to contact a tube advanced through the apparatus subsequent to contact by said one disc.

8. An apparatus for forming multiple lead helical fin formations as defined in claim 7, wherein the largest disc on said first group of discs is disposed adjacent said first spacer, and wherein said smallest disc of said third group of discs is disposed adjacent said second spacer and has a diameter substantially equal to the diameter of the largest disc of said first group of discs.

9. An apparatus for forming multiple lead helical fin formations as defined in claim 7 wherein each of said three groups of discs on each arbor comprise at least three discs of progressively increasing diameter.

0 ilk 4k 

1. Apparatus for forming a multiple lead helical fin formation on tubing which comprises: A. a plurality of arbors positioned in circumferentially spaced relation around the axis along which a tube advances during a progressive finning operation, said arbors being positioned at an angle to said tube axis; B. a plurality of finning discs mounted on each of said arbors for rotation therewith, said finning discs being mounted in three spaced groups of discs which sequentially engage a tube advanced through the apparatus; C. a pair of spacers mounted on each of said arbors, the first of said spacers separating the first group of discs to engage a tube advanced through the apparatus from the second group of discs to engage the tube, and the second of said spacers separating the second group of discs from the third group of discs to engage the tube, said spacers having an axial length sufficient to separate said groups of discs a distance greater than the thickness of at least three of the discs to provide a period of time between contact of a portion of the tube surface by the discs of the successive groups; D. the second of said three groups of discs including:
 1. a first disc adjacent said first spacer of a diameter less tHan the diameter of the largest disc of the first group of discs to engage the tube;
 2. said second group of discs including a last disc having a diameter greater than the diameter of the first disc of the second group of discs and larger than the diameter of the first disc adjacent said second spacer of the third group of discs to engage the tube; and
 3. said second group having another disc disposed intermediate said first disc and said second disc thereof, said other disc having a diameter intermediate the diameter of said first disc and said last disc of the second group of discs.
 2. said second group of discs including a last disc having a diameter greater than the diameter of the first disc of the second group of discs and larger than the diameter of the first disc adjacent said second spacer of the third group of discs to engage the tube; and
 2. An apparatus for forming multiple lead helical fin formations as defined in claim 1, wherein the last disc on said first group of discs has a diameter substantially equal to the diameter of the first disc on the third group of discs, and wherein said other disc of said second group of discs has a diameter substantially equal to the diameter of the last disc of the first group and the first disc of the third group.
 2. said second group of discs including another disc having a diameter greater than the diameter of said one disc of the second group and larger than the diameter of the smallest disc of the third group of discs to engage the tube, said other disc being arranged in said second group of discs to contact a tube advanced through the apparatus subsequent to contact by said one disc.
 3. said second group having another disc disposed intermediate said first disc and said second disc thereof, said other disc having a diameter intermediate the diameter of said first disc and said last disc of the second group of discs.
 3. An apparatus for forming multiple lead helical fin formations as defined in claim 1, wherein each of said arbors consists of identical sets of discs.
 4. An apparatus for forming multiple lead helical fin formations as defined in claim 1 wherein each of said three groups of discs on each arbor comprise at least three discs of progressively increasing diameter.
 5. An apparatus for forming multiple lead helical fin formations as defined in claim 1 wherein at least two of said arbors are axially located with respect to each other so that the tube engaging portions of corresponding discs lie in a plane perpendicular with the axis of the tube so that at least two leads of said fin formation are simultaneously formed by the first disc on different arbors.
 6. An apparatus for forming multiple lead helical fin formations as defined in claim 1 wherein said apparatus includes three of said arbors having identical sets of discs thereon, such arbors being axially located with respect to each other so that the tube engaging portions of corresponding discs lie in a plane perpendicular to the axis of the tube whereby three leads of said fin formation are simultaneously formed by the first disc on each of said three arbors.
 7. Apparatus for forming a multiple lead helical fin formation on tubing which comprises: A. a plurality of arbors positioned in circumferentially spaced relation around the axis along which a tube advances during a progressive finning operation, said arbors being positioned at an angle to said tube axis; B. a plurality of finning discs mounted on each of said arbors for rotation therewith, said finning discs being mounted in three spaced groups of discs which sequentially engage a tube advanced through the apparatus; C. a pair of spacers mounted on each of said arbors, the first of said spacers separating the first group of discs to engage a tube advanced through the apparatus from the second group of discs to engage the tube, and the second of said spacers separating the second group of discs from the third group of discs to engage the tube, said spacers having an axial length sufficient to separate said groups of discs a distance greater than the thickness of at least three of the discs to provide a period of time between contact of a portion of the tube surface by the discs of the successive groups; D. the second of said three groups of discs including:
 8. An apparatus for forming multiple lead helical fin formAtions as defined in claim 7, wherein the largest disc on said first group of discs is disposed adjacent said first spacer, and wherein said smallest disc of said third group of discs is disposed adjacent said second spacer and has a diameter substantially equal to the diameter of the largest disc of said first group of discs.
 9. An apparatus for forming multiple lead helical fin formations as defined in claim 7 wherein each of said three groups of discs on each arbor comprise at least three discs of progressively increasing diameter. 